• Journal of the Korean Chemical Society
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• v.34 no.5
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• pp.396-403
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• 1990

We describe how to design and construct a LPCVD (Low Pressure Chemical Vapor Deposition) apparatus which can be applicable to the study of reaction mechanism in general CVD experiments. With this apparatus we have attempted to make diamond like carbon films on the p-type (111) Si wafer from (H$_2$ ＋ CH$_4$) gas mixtures. Two different methods have been tried to get products. (1)The experiment was carried out in the reactor with two different inlet gas tubes. One coated with phosphoric acid was used for supplying microwave discharged hydrogen gas stream, and methane has been passed through the other tube without the microwave discharge. In this method we got only amorphous carbon cluster products. (2) The gas mixture (H$_2$ ＋ CH$_4$) has been passed through the discharge tube with the Si wafer located in and/or near the microwave plasma. In this case diamond-like carbon products could be obtained.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.48-48
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• 2009

최근 빠른 동작속도와 고 집적도를 얻기 위해 metal oxide semiconductor field effect transistor (MOSFET) 의 크기는 계속 해서 줄어들고 있다. 동시에 게이트의 절연층도 얇아지게 된다. 절연층으로 사용되는 $SiO_2$ 의 두께가 2nm 이하로 얇아 지게 되면 터널링에 의해 누설 전류가 발생하게 된다. 이 문제를 해결하기 위해 $SiO_2$ 를 대체할 고유전체 물질의 연구가 활발하다. 고유전체 물질 중에는 $ZrO_2,\;Al_2O_3,\;HfO_2$ 등이 많이 연구 되어 왔다. 하지만 유전상수 이외에 band gap energy, thermodynamic stability, recrystallization temperature 등의 특성이 좋지 않아 대체 물질로 문제점이 있다. 이를 보안하기 위해 산화물을 합금과 결합시키면 서로의 장점들이 합쳐져 기준들을 만족하는 물질을 만들 수 있고 $HfAlO_3$가 그 중 하나이다. Al를 첨가하는 이유는 문턱전압을 낮추기 위해서다. $HfAlO_3$는 유전상수 18.2, band gap energy 6.5 eV, recrystallization temperature 800 $^{\circ}C$이고 열역학적 특성이 안정적이다. 게이트 절연층은 전극과 기판사이에 적층구조를 이루고 있어 이방성인 드라이 에칭이 필요하고 공정 중 마스크물질과의 선택비가 높아야한다. 본 연구는 $HfAlO_3$박막을 $BCl_3/Ar,\;N_2/BCl_3/Ar$ 유도결합 플라즈마를 이용해 식각했다. 베이스 조건은 RF Power 500 W, DC-bias -100 V, 공정압력 15 mTorr, 기판온도 40 $^{\circ}C$ 이다. 가스비율, RF Power, DC-bias, 공정 압력에 의한 마스크물질과 의 선택비를 알아보았다.

• Journal of the Microelectronics and Packaging Society
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• v.14 no.3
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• pp.15-20
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• 2007

Low temperature processed ZnO-TFTs on glass below $270^{\circ}C$ for plastic substrate applications were fabricated and their electrical properties were investigated. Films in ZnO-TFTs with bottom gate configuration were made by RF magnetron sputtering system except for $SiO_2$ gate oxide deposited by ICP-CVD. ZnO channel films were grown on glass with various Ar and $O_2$ flow ratios. All of the fabricated ZnO-TFTs showed perfectly the enhancement mode operation, a high optical transmittance of above 80% in visible ranges of the spectrum. In the ZnO-TFTs with pure Ar process, the field effect mobility, threshold voltage, and on/off ratio were measured to be $1.2\;cm^2/Vs$, 8.5 V, and $5{\times}10^5$, respectively. These characteristic values are much higher than those of the ZnO-TFTs of which ZnO channel layers were processed with additional $O_2$ gas. In addition, ZnO-TFT with pure Af process showed smaller swing voltage of 1.86v/decade compared to those with $Ar+O_2$ process.

• Journal of the Korean Vacuum Society
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• v.14 no.3
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• pp.147-152
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• 2005

The structural evolution of $Ni(400\;\AA)/Au(400\;\AA)$ films on p-type GaN during thermal oxidation in ai. was investigated by in situ x-ray scattering experiments. These results indicate that Ni layer and Au layer intermix during thermal oxidation. Au-rich solid solutions containing the different amount of Ni atoms are formed during oxidation. The Ni atoms in Au-rich solid solution out-diffuse as the oxidation proceeds resulting in the formation of NiO(111) phase. Despite of the complete oxidation at $650^{\circ}C$, the position of bulk Au(111) diffraction profile indicates that small amount of Wi atoms are still incorporated in the Au phase.

• Korean Journal of Materials Research
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• v.1 no.4
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• pp.191-197
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• 1991

The surface roughnesses of titanium silicide films and the diffusion behaviours of dopants in single crystal and polycrystalline silicon substrates durng titanium silicide formation by rapid thermal annealing(RTA) of sputter deposited Ti-filicide film from the composite $TiSi_{2.6}$ target were investigated by the secondary ion mass spectrometry(SIMS), a four-point probe, X-ray diffraction, and surface roughness measurements. The as-deposited films were amorphous but film prepared on single silicon substrate crystallized to the orthorhombic $TiSi_2$(C54 structure) upon rapid thermal annealing(RTA) at $800^{\circ}C$ for 20sec. There was no significant out-diffusion of dopants from both single crystal and polycrystalline silicon substrate into titanum silicide layers during annealing. Most of the implanted dopants piled up near the titanium silicide/silicon interface. The surface roughnesses of titanium silicide films were in the range between 16 and 22nm.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.12
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• pp.1122-1127
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• 1998

Group II-AF_2$films such as $CaF_2$, $SrF_2$, and $BaF_2$ have been commonly used many practical applications such as silicon on insulatro(SOI), three-dimensional integrated circuits, buffer layers, and gate dielectrics in filed effect transistor. This paper presents electrical and structural properties of fluoride films as a gate dielectric layer. Conventional gate dielectric materials of TFTs like oxide group exhibited problems on high interface trap charge density($D_it$), and interface state incorporation with O-H bond created by mobile hydrogen and oxygen atoms. To overcome such problems in conventional gate insulators, we have investigated $CaF_2$ films on Si substrates. Fluoride films were deposited using a high vacuum evaporation method on the Si and glass substrate. $CaF_2$ films were preferentially grown in (200) plane direction at room temperature. We were able to achieve a minimum lattice mismatch of 0.74% between Si and $CaF_2$ films. Average roughness of $CaF_2$ films was decreased from 54.1 ${\AA}$ to 8.40 ${\AA}$ as temperature increased form RT and $300^{\circ}C$. Well fabricated MIM device showed breakdown electric field of 1.27 MV/cm and low leakage current of $10^{-10}$ A/$cm^2$. Interface trap charge density between $CaF_2$ film and Si substrate was as low as $1.8{\times}10^{11}cm^{-2}eV^{-1}$.

• Journal of the Korean Magnetics Society
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• v.16 no.1
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• pp.23-27
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• 2006

By substituting Mn or Cr for Co in inverse spinel $CoFe_2O_4,\;Mn_xCo_{1-x}Fe_2O_4\;and\;Cr_xCo_{1-x}Fe_2O_4$ and thin films were prepared by sol-gel method and their structural and magnetic properties were investigated. X-ray diffraction indicates that the cubic lattice constant increase for the Mn substitution while it hardly changes for the Cr substitution. Substitution of $Mn^{2+}$ for octahedral $Co^{2+}$ sites can explain the increase of lattice constant in $Mn_xCo_{1-x}Fe_2O_4$. On the other hand, Substitution of $Cr^{3+}$ for octahedral $Co^{2+}$ and subsequent reduction of $Fe^{3+}$ ion into $Fe^{2+}$ are expected to happen. Mossbauer spectroscopy measurements on $Cr_xCo_{1-x}Fe_2P_4$ indicate the existence of tetrahedral $Fe^{2+}$ ions that are created through reduction of tetrahedral $Fe^{3+}$ ions in order to compensate charge imbalance happened by $Cr^{3+}$ substitution for octahedral $Co^{2+}$ sites. On the other hand, no $Fe^{2+}$ ions were detected by Mossbauer spectroscopy for $Mn_xCo_{1-x}Fe_2O_4$. A migration of $Fe^{3+}$ ions from octahedral to tetrahedral sites In $Mn_xCo_{1-x}Fe_2O_4$ was detected by Mossbauer spectroscopy for x>0.47. Vibrating sample magnetometry measurements on the samples at room temperature revealed that the saturation magnetization increases by Mn and Cr substitution for certain range of x, qualitatively explainable in terms of the comparison of spin magnetic moment among the related transition-metal ions.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.11 no.2
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• pp.225-229
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• 2011

In this study, capacitive type pressure sensors based on low temperature co-fired ceramics (LTCC) technology for environmental monitoring were demonstrated. The LTCC is one of promising technology than is based one since it has many advantages (e.g., low cost production, high manufacturing yields and easy realizing 3D structure etc.) for sensor application. Especially, it has good mechanical and chemical properties for robust environmental application. The 3D LTCC diaphragm with thickness of 400 ${\mu}m$ were fabricated by laminating 4 green sheets using commercial powder (NEG, MLS 22C). To evaluate the sensing properties of the different cavity areas, two types of diaphragm which had different cavity areas with 25, 49 $mm^2$ respectively, were fabricated. To realize capacitive type pressure sensor, the Au top electrode was fabricated using thermal evaporator and the bottome electrode was compressed using aluminium foil. The sensing properties of the fabricated sensors showed linear characteristic under different pressure (0~30 psi) using pressure measurement system.

• Proceedings of the Materials Research Society of Korea Conference
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• 2009.05a
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• pp.30.2-30.2
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• 2009

TiO2는 3가지의 결정구조를 가지고 있으며 결정 입자, 구조, 상의 형태에 따라서 성질 및 기능에 영향을 주고 있다. anatase상의 애너지 밴드갭과 전자와의 재결합 확률이 크기 때문에 Rutile상 보다 우수한 성질을 갖고 있어 산화물 반도체로 이용하는 것이 적합하다. 본 실험에서는 나노로드의 TiO2를 수열처리법에 의해 합성한 후 박막을 제조하여 감응특성을 조사하였다. X선 회절분석기(X-Ray Diffraction)로 분석결과 ph=1의 루타일상을 제외하고, pH=2~7의 더 넓은 구간에서 뚜렷한 회절피크의 anatase 상이 나타났으며 다른 비정질상이 발생되지 않는 결정성이 좋은 단결정임이 나타났다. NaOH solution 을 이용하여 수열처리후 $180^{\circ}C$이상의 특정 온도 구간에서 수십 나노 로드 형태로의 2차 성장된 모습을 TEM과 EDS로 결정구조와 화학조성을 분석하였다. 그리고 BET 측정을 통해 $180^{\circ}C$의 소성온도에서 TiO2 입자의 비표면적이 가장 우수한 것으로 나타났다. 나노로드의 수용액을 Al2O3기판의 감지막 위에 떨어뜨려 네트워크된 막을 형성한후에 센서를 제작하였다. 히터 전압이 $400^{\circ}C$에서 나노 파우더센서에서는 반응이 일어나지 않은 반면, 나노 로드센서는 CH3SH에서 28% 의 높은 감도를 얻었고, Toluene의 반응에서는 15%의 감도가 나타났다. 그 외 NO, CO, H2등의 측정에서 아무런 반응이 일어나지 않았다. 이는 비교적 기공이 큰분자(Size)를 가진 CH3SH=76nm, Toluene=60nm에서 반응이 일어난 반면, H2=28nm, CO=22nm에서 감도가 나타나지 않은 것을 보아 흡착분자크기에 의한 영향이 큰 것으로 나타났다.

• Proceedings of the KIEE Conference
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• 2006.07c
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• pp.1637-1638
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• 2006

HVAC 시스템은 쾌적하고 깨끗한 운전환경을 만들어 줌으로써 운전자에게 향상된 안락성과 안전성을 제공한다. 이때 센서는 시시각각으로 변화하는 차실 내외의 환경변화에 대한 정보를 검출하여 HVAC 제어 유니트에 제공한다. 현재 HVAC 시스템에 사용되고 있는 후막 가스센서는 소자 크기와 소비전력이 크고, 제작공정이 까다로워 생산성이 낮은 단점이 있다. 이와 같은 문제점을 해결하기 위해서 최근에는 초소형화, 저소비전력, 대량생산에 의한 저가격화가 가능한 MEMS 가스센서의 연구개발이 활발히 진행되고 있다. 본 연구에서는 MEMS 구조체를 이용한 마이크로 가스센서를 설계 및 제작하였고, 감도특성을 고찰하였다. 가스 감지막은 금속산화물 페이스트를 스크린 프린팅 하는 종래의 방법 대신 MEMS 구조체에 적용 가능한 sol-gel 프로세스에 의해 형성하였다. 또 가스 감지전극과 micro-heater를 동일 평면상에 제작, 공정을 간소화하여 저가화를 시도하였다. MEMS 구조체 위에 제작된 Pt 박막 micro-heater의 인가전압에 따른 발열특성을 조사한 결과, 발열온도가 인가전압에 비례하는 이상적인 선형성을 나타내었으며, $300^{\circ}C$의 동작 온도에 도달하기 위해 65mW 이하의 저전력 동작이 가능하였다. 가스 센서의 감도특성 확인 실험은 CO 가스 10ppm, NO 가스 0.3ppm을 기준으로 수행되었으며, CO 및 NO에 대해 Rs(sensitivity, 가스반응저항/초기저항) 값은 각각 0.753 과 2.416로 우수한 성능을 나타내었다.